The present invention relates to the technology of a speaker driving apparatus.
In the two-channel stereo audio equipment in the related art, two speakers are positioned on the right and left sides at a distance to some extent and also a stereo left channel signal and a stereo right channel signal are supplied to a stereo speaker and a right speaker respectively. Then, when a listener takes a position in a front center area between two channels, such listener can recognize an echolocation of a sound image in the lateral direction.
Further, the so-called 5.1 channel surround audio system in which three channels on the front center, rear left, and rear right sides and the channel for a low-pitched sound, for example, are provided in addition to two channels in the related art is spreading. With this arrangement, the listener can recognize echolocations of the sound image on the right and left and backwards and forwards and can experience the acoustic effects with the ambience of the scene. This acoustic effect is called the surround effect.
However, in the above surround audio system, there existed such problems that a space having some size is needed because a total of six speakers must be arranged around the listener and also a cost is increased owing to an increase of the speakers.
Therefore, the technology to bring about the surround effect by two-channel stereo audio signals has been proposed. For example, in the technology disclosed in JP-B-3-80400, a predetermined amplitude gain and a predetermined amount of phase change are set to the stereo input signals on two right and left channels and also reverse characteristics of the amplitude gain and an amount of phase change are provided with a simple structure. According to this technology, a sound field having the surround effect can be reproduced faithfully to an original sound by using the two-channel stereo audio equipment. Also, the surround effect can be produced even when a distance between the right and left speakers is small.
However, even though the technology set forth in JP-B-3-80400 is applied, no change is caused in such a situation that an area in which the listener can recognize the sound field accompanied by the surround effect is still limited around the front center between the right and left speakers. As a result, when a distance between the right and left speakers is small, an area in which the listener can recognize a sound field to produce the surround effect is very narrow. Also, it is impossible for a plurality of listeners to enjoy the surround effect simultaneously.